"No modems detected..." message. Can't connect.

I recently bought a new computer from Dell with Windows XP
Home Edition, and upgraded myself to XP Pro. Now I can't,
for the life of me, connect to the Web. I can't do
anything with the modem, really. When I try and sign up
for MSN, I get the following message: "No modems detected,
please install a modem before continuing."

The modem is installed correctly. The device manager shows
the modem just fine. I've gone through many things with
Dell and MSN tech support people, including uninstalling
and reinstalling the drivers, moving the PCI modem card to
another slot, even putting in other modems, but all with
the same result. I've used a "Modem Helper" application
that ships with my computer, and it says the modem is
working properly... I even hear the dial tone when using
that application, but when it comes to using the OS or MSN
Explorer, I get the same "No modems detected..." error
message.

Someone please help. I don't want to restore the computer
with the manufacturer discs if at all possible.

Thanks --Cary